1. Field of the Invention
The present invention relates generally to an apparatus for providing route guidance information and to a communication terminal receiving route guidance information from the apparatus for providing route guidance information. The present invention also relates to a system for providing route guidance information comprising the apparatus for providing route guidance information and the communication terminal.
2. Description of the Related Art
As a system for providing route guidance information to a communication terminal, Japanese Patent Laid-Open Publication No. Hei 9-178499, for example, discloses a route information providing system. In the system disclosed in that publication, route calculation data is sent from an in-vehicle device to an information center and specific route guidance information is sent from the center to the in-vehicle device in batch transfer processing.
In such a system, however, the batch transfer processing for sending route guidance information from the center to the in-vehicle device leads to certain problems. One resulting problem is that there is a possibility that it may become impossible to execute route guidance when a portion of the route guidance information is lost, such as through a communications failure occurring while sending the route guidance information. Another resulting problem is the excessive time and cost required for transmission because data of basically less importance for the communication terminal is transmitted in the batch transfer processing.
Therefore, it is an object of the present invention to provide executable route guidance, even when a communication failure occurs during transmission of the route guidance information. The object is achieved in the present invention by reorganizing a plurality of practical units of guide information from a route guide information and sequentially sending the practical units of guide information to a communication terminal. Therefore, route guidance can be executed based on that portion of practical units received in the event of a communication failure.
With the present invention, it is possible to send route guidance information data of a reduced size by selecting information according to circumstances. As a result, communication connection time and associated costs can be reduced and reliability of route guidance in the event of a breakdown in communication can be improved.
With the present invention, it is also possible to send route guidance information data of a reduced size by selecting a guidance position where a route is actually instructed as circumstances demand from potential guidance positions which are possible positions where a route is instructed. This leads to reduction of a time and costs of communication and improvement the rate of implementing route guidance at the occurrence of a breakdown of communication as well.
Furthermore, it is possible to send route guidance information of which data size is adjusted by calibrating an effective segment length in this invention. This also leads to a reduction of time and costs of communication and improvement of the rate of implementing route guidance at the occurrence of a breakdown of communication.
In the present invention, it is also possible to send route guidance information of which data size is adjusted by selecting a data format in which information is structured with appropriate size when a plurality of data formats are applicable to an information element. This results in improving the rate of implementing route guidance at the occurrence of a breakdown of communication.